/*
 * **** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is part of dcm4che, an implementation of DICOM(TM) in
 * Java(TM), hosted at https://github.com/dcm4che.
 *
 * The Initial Developer of the Original Code is
 * J4Care.
 * Portions created by the Initial Developer are Copyright (C) 2015-2018
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 * See @authors listed below
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * **** END LICENSE BLOCK *****
 *
 */

package org.dcm4che3.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.net.InetAddress;

/**
 * @author Gunter Zeilinger <gunterze@gmail.com>
 * @since Apr 2018
 */
public class ReverseDNS {
    static final Logger LOG = LoggerFactory.getLogger(ReverseDNS.class);
    static final boolean DISABLED = isFalse(ReverseDNS.class.getName());

    private ReverseDNS() {}

    private static boolean isFalse(String name) {
        try {
            String s = System.getProperty(name);
            return ((s != null) && s.equalsIgnoreCase("false"));
        } catch (IllegalArgumentException | NullPointerException e) {
        }
        return false;
    }

    public static String hostNameOf(InetAddress inetAddress) {
        if (DISABLED)
            return inetAddress.getHostAddress();

        if (!LOG.isDebugEnabled())
            return inetAddress.getHostName();

        String hostAddress = inetAddress.getHostAddress();
        LOG.debug("rDNS {} -> ...", hostAddress);
        long start = System.nanoTime();
        String hostName = inetAddress.getHostName();
        long end = System.nanoTime();
        LOG.debug("rDNS {} -> {} in {} ms", hostAddress, hostName, (end - start) / 1000);
        return hostName;
    }
}
